Tubular heat exchanger for indirectly cooling combustion gases from refuse incinerators



United States Patent Inventors Otto Salamon Zurich; Herbert Petry, Trimbach, Switzerland AppLNo. 774,833 Filed Nov. 12, 1968 Patented 0ct.13,l970 Assignee Von RollA.G.,

Gerlafingen, Switzerland a corporation of Switzerland Priority June 6,1968

Switzerland 8,348/68 TUBULAR HEAT EXCHANGER FOR INDIRECTLY COOLING COMBUSTION GASES FROMREFUSE Primary Examiner-Robert A. O'Leary Assistant E.taminerTheophil W. Streule ABSTRACT: A novel tubular heat exchanger is disclosed in combination with a refuse incinerator for indirectly cooling the combustion gases of said incinerator. by means of cold air serving as the cooling agent. The inventive heat exchanger comprises a plurality of vertical steel tubes for the upward passage of the combustion gases which are mounted within a casing. while the cooling air is supplied in two streams flowing crosswise with respect to said vertical tubes. The volume of one of the air streams is controlled in dependence upon the outlet temperature of the cooled combustion gases. An alternative embodiment with transversally finned tubes is also disclosed.

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Sheet 2 of 2 IN VENTOR$ 07'7'0 My -/%4klr cney ATTORNEYJ' TUBULAR HEAT EXCHANGER FOR INDIRECTLY COOLING COMBUSTION GASES FROM REFUSE INCINERATORS BACKGROUND OF THE INVENTION The present invention relates to a new and improved tubular heat exchanger and. in its more specific aspects. relates to such a tubular heat exchanger which is employed for the'indirect cooling of cumbustion gases emanating from refuse in cinerators by utilizing cold air as the cooling agent to absorb through convection part of the heat content of such combustion gases.

Considering the inventive heat exchanger in its broader physical construction it will be seen to comprise a steel plate casing having both ends closed and equipped with inlet and outlet apertures for the stream of combustion gases which are to be cooled. A plurality of essentially vertically extending steel tubes are located within the casing. These tubes have their lower ends fastened, as by welding, in holes of corresponding size provided at the bottom of the casing and their upper ends pass with a small clearance through similar holes provided at the cover of the casing. The combustion gases which are to be processed flow in upward direction within these tubes. Furthermore, lateral inlet and outlet connections are provided for the cooling air.

Similar type heat exchangers are well known to the art, oftentimes being used for cooling the combustion gases emanating from refuse incinerators. Generally, they comprise a cylindrical casing with closed ends and upper and lower chambers for the inflowing and outflowing stream of cases, the direction of flow usually being downward. In such heat exchangers the cooling air flows parallel to the gases, either in the same or in an opposed direction. A zig-zag flow of the cooling air is obtained by the provision of conveniently placed baffles. This is done in order to increase the length of the flow path and the duration of contact. With such heat exchangers the temperature of the combustion gases may be reduced from approximately I800F. at the outlet of the incinerator down to about 550 to 650F., this representing the maximum range of tem perature ensuring for efficient gas cleaning.

Although from an engineering standpoint the conception of such heat exchangers is correct and notwithstanding the fact that they are reliable in operation, they still possess certain drawbacks. One of these is the high consumption of energy required for the transport of both the gases and the cooling air due to the high drop in the pressure head owing to the long flow paths and the multiple changes in the flow direction for the air stream. Furthermore, the cooling effect can only be controlled with great difficulty and with extreme delay. There does not exist any prompt response to the varying load and temperature conditions as such frequently occur in any refuse incinerator. This is due to the well known fact that simple or multiple dampers, as such are usually provided, are ineffective for precise regulation of anygaseous stream of large volume as would be the case with the cooling air. Consequently, the out let temperature of the cooled gases is not constant, rather varies within wide limits, resulting in unstable operational conditions for costly equipment such as electrostatic precipitators, draught fans, and so forth.

SUMMARY. OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a heat exchanger which effectivelyovercomes the aforementioned drawbacks of the prior art structures.

Another, more specific object of the present invention relates to the provision of an improved construction of heat exchanger used in conjunction with a refuse incinerator for indirectly cooling the combustion gases effluent therefrom, cold air serving as the cooling agent, and wherein the heat exchanger is capable of readily adapting the cooling effect to the variable load and temperature conditions prevailing in the incinerator, so as to keep the outlet temperature of the cooled combustion gases within prescribed limits.

Still a further significant object of the present invention is directed at providing an improved heat exchanger readily capable of use for the cooling of combustion gases, wherein the operation of the heat exchangerand thecooling action undertaken thereby can be carried out in airnuch more controlled fashion, resulting in improved operating conditions, less energy consumption, and a more efficient cooling phenomena.

In order to implement the foregoing objects, the inventive heat exchanger departs from the prior art constructions in that the inlet and outlet of the combustion gases is through the bottom and cover, respectively, of the heat exchanger. Furthermore, the flow path for the cooling air is substantially straight or linear and is directed crosswise of the tubes provided for the combustion gases themselves, with inflow and outflow connections being placed on opposed sides of the casing. According to a further aspect of the invention there may be provided a partition wall which is advantageously located approximately at the central region or at one half the length of the tubes and which extends substantially perpendicular to the axes of such tubes. This partition wall defines channels within the casing for two distinct streams of cooling air, each air stream being propelled by a separate fan. Additionally, a regulating device is provided for the purpose of controlling the volume of one ofthe streams of cold air, preferably the upper stream. This regulating device is controlled as a function of the outlet temperature of the cooled combustion gases, such control being undertaken either manually or automatically, in order to keep the outlet temperature at'a constant level within prescribed limits.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood, and objects other than those set forth above, will become apparent, when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIG. la is a schematic longitudinal sectional view of a preferred embodiment of inventive heat exchanger;

FIG. Ib is a front view of the heat exchanger of FIG. la as viewed in the direction of the arrow B of FIG. la;

FIG. 1c is a plan view of the heat exchanger depicted in FIG. Ia;

FIG. 2 schematically illustrates the invetive heat exchanger used in conjunction with a refuse incinerator shown schematically in longitudinal sectional view, the heat exchanger being depicted as mounted on top of such incinerator; I

FIG. 3a is an enlarged fragmentary longitudinal sectional view of a modified form of tubing used in the heat exchanger of the present invention; and

-FIG'. 3b is a plan view partly in cross section of the heat exchanger tube shown in FIG. 3a.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, in the exemplary emodiment depicted in FIG. la, the heat exchanger is its entirety has been conveniently designated by reference character WA. This heat exchanger WA incorporates a steel casing 1 closed by the upper and lower end plates 2 and 2', respectively. Steel heat exchanger tubes 3 are arranged in vertical disposition within the casing l. The lower ends of the tubes 3 are fastened, as by welding, in corresponding holes, schematically indicated by reference character 2a provided at the lower end plate 2, whereas the upper ends of such tubes 3 pass freely with a minimum clearance through corresponding holes or apertures 2b provided at the upper end plate or cover 2. Furthermore, by referring again to FIG. la it will be seen that a transversely extending steel plate 7 is located approximately at the center or half-length of these tubes 3, this plate 7 being arranged substantially perpendicular to the lengthwise axes A of the tubing 3. At the .upper end of the heat exchanger WA there is provided the outlet connection 4 for the cooled combustion gases. Additionally, laterally to one side or end of the heat exchanger there are further provided the inlet connections 6 and 6 for the two streams of cooling air which flow in a straight line through the interior of the casing I to emanate from the respective outlet connectionsand 5'.

Through the use of conventional means or techniques, such as the insufflation or blowing of cold air, as will be explained more fully hereinafter, or by any other well known means, the

temperature of the combustion gases flowing out of the incinerator can be limited to about I500F. These gases enter the heat exchanger WA, as indicated by the arrows 10, to flow upwards through the tubing 3 and to be cooled therein. The temperature of these gases at the level of the partition wall 7 is approximately 950F. and amounts to about 660F. at the outlet of such heat exchanger, as indicated by the arrows 11.

The invention contemplates the use of a fan 13 to absorb cold air at its suction side, as indicated by the arrows 12 in FIG. Ia, and this fan 13 supplies a stream of cold air through the lower partition or chamber 50 of the heat exchanger WA. This stream of air, which will be conveniently referred to hereinafter as basic stream, enters the interior of the casing or housing 1 by means of the lower connection or inlet 6 and flows within the heat exchanger and belowthe partition wall 7 in a substantially straight flow path which is directed crosswise or transverse to the lengthwise extension of the tubes 3, whereafter it is eventually expelled or discharged from this casing 1 through the outlet or connection 6' and, in so doing, this air stream is heated to a temperature of about 300F.

A second fan 17 absorbs cold air at its suction side, as indicated by the arrows 15 in FIG. 1a, this fan being provided with a suitable regulating device 16 in order to control the volume of the air. In the exemplary emodiment of FIG. 1a the regulating device 16 is constituted by a multiple damper. This fan 17 supplies a second stream of cooling air, hereinafter conveniently referred to as the regulating stream." In a fashion similar to the basic stream, this regulating stream of cooling air also enters the interior of the casing 1. this time however through the upper inlet or connection 5, flowing within the heat exchanger proper and above the partition wall 7 in the compartment or chamber 51, in a substantially straight path of flow which again is crosswise or transverse to the lengthwise axes of the tubes 3, eventually leaving the chamber 51 by means of the outlet connection 5', as indicated by the arrows 14'. This regulating stream is also likewise heated to a temperature of about 300F.

The two air streams 14 and 14 flowing out of the heat exchanger WA may be united into a single stream at a common conduit, which, for convenience in illustration has not been shown, or else expelled into the atmosphere, or conducted as a hot underblast beneath the combustion grate of the incinerator. The latter procedure is recommendable in the event that low grade or very wet refuse has to be incinerated.

The regulating device 16 controlling the 'air volume of the "regulating stream," which can be designated by reference numerals 15-14, is in turn governed by the outlet temperature of the cooled combustion gases, as measured at the outlet location 11 and which has to be maintained at a level of approximately 660F. In the exemplary embodiment shown, there can be conveniently provided at this outlet location 11 a standard temperature sensing device 52 which, for instance, delivers a suitable signal to a conventional control unit 53 influencing the operation of the regulating device 16 as a function of the outlet temperature at the heat exchanger WA as sensed by the temperature sensing device 52. In this way it is possible to effectively control the air volume of the regulating stream.

Turning now to the combined arrangement of heat exchanger and refuse incinerator as shown in FIG. 2 it will be recognized that the inventive tubular heat exchanger 107 is shown mounted on top of a refuse incinerator, generally designated by reference numeral 120. The refuse incinerator 120 is formed of refractory brickwork 100 and incorporates a charging pit 101 for the refuse to be combusted or incinerated. Such refuse is incinerated upon a combustion grate 102 disposed within a combustion chamber 103. Secondary cold air is introduced into the combustion chamber 103 through the inlet aperture or'port 105, this secondary air serving to maintain the temperature prevailing within the combustion chamber 103 below I500-F. as mentioned previously. The supply of secondary air which has been shown by the arrow 109, can be controlled automatically as a function of the temperature of the combustion gases as measured at the incinerator outlet aperture or port 106, in accordance with conventional techniques. Such need not be explained in any greater detail since the present invention is not concerned with the supply of such secondary air and the particular measures involved are not necessaryfor understanding the inventive concepts. Continuing, it will be understood that the noncombustible residues of combustion (the clinker for instance) are discharged from the lower end of the combustion grate 102, through a pit 115 in the usual fashion.

The combustion gases themselves flow through the outlet aperture or port 106, thereby entering the tubes of the heat exchanger 107 which are not visible in this figure but may be assumed to be of the type shown in conjunction with FIGS. 1a to 1c inclusive. Upon entering the tubes the combustion gases flow upwards and leave the heat exchanger as indicated by the arrows 110, but it will be recalled they have been cooled to approximately 660F. in the manner previously considered. In FIG. 2 the reference numerals 111-112 designate the inflow and outflow of the basic stream of cooling air, the numerals 1131l4 the inflow and outflow of the regulating stream of cooling air. These two streams of cooling air are in parallel with one another, entering the heat exchanger 107 at the inlet connections 111 and 113, respectively, possessing an ambient temperature of approximately 60--70F. and leaving such heat exchanger at the outlet or discharge locations 112 and 114, respectively, but again it will be recalled, heated to approximately 300F. as previously explained. As also heretofore mentioned, the thus heated basic stream and regulating stream of cooling air will eventually either be expelled directly into the atmosphere or ducted below the combustion grate 102 in order to serve as a hot underblast.

In FIG. 3a there is depicted a modified form of heat I exchanger tube as contemplated for use in the inventive heat exchanger. In order to simplify the showing in the drawings, only one of these tubes 200 has been represented in longitudinal section in FIG. 3a and such tube is also shown in partial cross section in FIG. 3b. It will be seen that the tube 200 itself is equipped with transverse extending tins 201. These fins 201 are affixed, as by welding, to all of the tubes 200 at equal intervals, their primary purpose being to increase the active surface of the tubes with a view toward better heat transmission, thereby reducing the overall dimension of the heat exchanger for a given capacity. By employing fins 201 of sufficient size, as schematically represented in FIG. 3b, approximately corresponding to the spacing or intervals between the tubes, these tins provide between themselves parallel channels for the streams of cooling air and even permit the transverse partition wall 7 used in the arrangement of FIG. la to be dispensed with. This constitutes a further advantage of the modified form of heat exchanger tubing depicted in FIGS. 3a and 3b.

Apart from the previously mentioned advantages of the inventive heat exchanger and the objectives which are realized through the physical construction thereof, the heat exchanger as contemplated by this invention provides a compact unit of moderate weight and size and of corresponding moderate cost, possessing high cooling efficiency due to the optimum conditions therein for the transmission of heat, with the streams of cooling air flowing crosswise to the axes of the tubes. A further notable advantage resides in the reduced drop in the pressure head for both the combustion gases and the cooling air due to the fact that the flow paths which are provided are straight and of reduced length. The drop in the pressure head for the cooling air may be further reduced by arranging the heat exchanger tubes in alignment in the direction of flow of the air, as schematically depicted in FIGS la and la for instance.

Furthermore. by dividing the total volume of cooling air into two distinct streams only one of which is subject to being regulated, the regulation can be carried out in a more precise manner and with much quicker response characteristics, so as to effectively adapt the cooling effect to the variable conditions of the incineration process. This enables the outlet temperature of the combustion gases to be maintained at a prescribed level within narrow limits.

Finally, it is or significance to mention that the regulation device 16 of FIG. 1a which is contemplated to constitute a multiple damper and serves for the regulation or control of part of the cooling air, can be conveniently replaced by any other known device or means serving the same purpose, such as by using a variable speed motor 54 for driving the fan 17, as shown in phantom lines in FIG. la. Such variable speed drive motor 54 can be operated as a function of the outlet temperature of the cooled combustion gases as sensed by the temperature sensing device 52. Furthermore, it might be mentioned that instead of using an automatic control for the regulation device as previously explained, manual control thereof would also be possible.

it should be apparent from the foregoing detailed description, that the objects set forth at the outset to the specification, have been successfully achieved.

We claim:

1. A tubular heat exchanger especially for the indirect cooling ofcombustion gases emanating from refuse incinerators by means of cold air serving as a cooling agent, said heat exchanger comprising a steel plate casing closed at both its upper and lower ends, a plurality of linear steel tubes disposed within said casing in substantially vertical arrangement for the upward passage therethrough of the combustion gases to be cooled, said tubes having their lower ends welded in corresponding holes provided in the bottom wall of said casing and their upper ends passing freely with minimum clearance through corresponding holes provided in the top wall of said casing, said casing including a pair of lateral connections on each of two opposite sides of said casing defining inflow and outflow connections for two streams of cooling air, a transverse extending partition wall extending perpendicular to the lengthwise axes of said tubes and located about half-length of them, thereby defining a separate and straight flow path for each of said two streams of cooling air, said two flow paths being in parallel with one another and being directed crosswise of said tubes and past said tubes once between said respective inlet and outlet opening pairs, 'one flow path of said two flow paths comprising a basic stream of cooling air having a constant air volume. and the other flow path comprising a regulating stream of cooling air, said tubes being arranged in rows aligned with said two flow paths of said two streams of cooling air, two separate fans for separately driving said two streams of cooling air a regulating device for controlling the air volume flow rate provided only for said fan driving said regulating stream of cooling air, a temperature sensing device provided at an outlet location of the cooled combustion gases for detecting the temperature of said cooled combustion gases at the outlet of said heat exchanger, said temperature sensing device being connected to a control unit for influencing the operation of said regulating device as a function of said outlet temperature of said cooled combustion gases so as to automatically maintain said outlet temperature of said cooled combustion gases at a prescribed level within narrow limits.

2. A tubular heat exchanger as defined in claim 1, wherein a plurality of transverse extending fins extend perpendicular to the lengthwise axes of and are attached to said tubes at equal intervals, the size of said fins corresponding approximately to the intervals between adjacent tubes thereby defining a plurality of parallel channels for the cooling air.

3. A tubular heat exchanger as defined in claim 1, including means for variably controlling the rotational speed only of said fan provided with said regulating device so as to control said speed in dependence upon said outlet temperature of said cooled combustion gases. 

